Rick Perry points to a member of the audience during a break in the Republican presidential candidate debate at Saint Anselm College in Manchester, N.H., Saturday, Jan. 7, 2012.

Rick Perry points to a member of the audience during a break in the Republican presidential candidate debate at Saint Anselm College in Manchester, N.H., Saturday, Jan. 7, 2012.

Photo: Elise Amendola / Associated Press

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Rick Perry answers a question as Newt Gingrich listens in the background during a Republican presidential candidate debate at the Capitol Center for the Arts in Concord, N.H., Sunday, Jan. 8, 2012.

Rick Perry answers a question as Newt Gingrich listens in the background during a Republican presidential candidate debate at the Capitol Center for the Arts in Concord, N.H., Sunday, Jan. 8, 2012.

Photo: Charles Krupa / Associated Press

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Texas Gov. Rick Perry and his fellow Republican presidential candidates walk on the stage and are greeted by moderator David Gregory prior to the NBC News Facebook Debate on 'Meet the Press' January 8, 2012 at the Capitol Center for the Arts in Concord, N.H. less

Texas Gov. Rick Perry and his fellow Republican presidential candidates walk on the stage and are greeted by moderator David Gregory prior to the NBC News Facebook Debate on 'Meet the Press' January 8, 2012 at ... more

New e-book claims Rick Perry was under influence of painkillers during debates (with PHOTO GALLERY)

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The whispers have been going around Washington and Austin for months: Rick Perry’s less-than-stellar performances in Republican presidential debates could be attributed to the use of painkillers. Now, the unconfirmed theory is mentioned in a soon-to-be released e-book entitled “Inside the Circus.”

According to authors Mike Allen and Evan Thomas, Perry used medication during the debates to relieve severe back pain, The Daily Caller reported. Allen is the chief White House correspondent for Politico and Thomas is an award-winning journalist and former assistant managing editor for Newsweek.

“It became an open secret that he was using painkillers in sufficient dosages to keep him standing through the two-hour debates,” the book states.

NBC’s Carrie Dann tweeted that Perry’s adviser, Ray Sullivan, responded to the claims and said they were “irresponsible, unsourced and unfounded … false, unsubstantiated.”

The Texas governor underwent back surgery in July and acknowledged that back pain played a role in his shaky performance early on.

He told the Des Moines Register in December, ” I think part of the reason you have seen a somewhat different candidate on the debates is my health, and (I’m) both physically and mentally just back in the game,” he said. “You have fusion on your back, and it takes you a while to get back on your game.”

However, he did not use the ailment as an excuse for his major “oops” moments, including when he forgot one of the federal agencies he would cut and how many justices serve on the Supreme Court.

The authors describe a moment at a debate in New Hampshire where another candidate’s campaign manager overheard Perry singing “I’ve been Working on the Railroad” in the bathroom.

“Wondering who was making all the noise, the campaign manager turned his head and saw, to his surprise, the governor of Texas,” Allen and Thomas write. “Nonplussed, the campaign manager made a hasty exit; as the bathroom door closed, he could hear Perry still merrily singing away: ‘I-I-I’ve been working on the ra-a-i-i-l-road, all-l-l the live-long day . . .’”